1. Field of the Invention
This invention relates to a method of producing a calcium-enriched aseptic soy bean curd. More particularly, it relates to a method of producing a calcium-enriched aseptic soy bean curd in which a calcium hydroxide-sucrose complex hitherto not used as a coagulant for the soy bean curd is used for the first time as such coagulant.
2. Description of the Prior Art
Heretofore, calcium sulfate or "bittern" consisting of a mixture of magnesium chloride and magnesium sulfate, have been used as a coagulant for preparation of the soy bean curd. In recent years, the soy bean curd packaged in blow molded containers are manufactured using glucono-delta-lactone (abbreviated as the GDL) as coagulant. With these methods, however, the soy bean curd may be sterilized insufficiently and has a rather short shelf life.
In order to obviate such drawbacks, a method of producing an aseptic soy bean curd packaged in a container has been shown and described in the Japanese Patent Kokoku Nos. 56-23574 and 56-23577. According to this method, the soy bean milk is sterilized by the ultra high temperature treatment (UHT) system (for example the vacuum thermo injection system VTIS). Then, the coagulant (GDL) is added thereto under an aseptic atmosphere, the resulting product is subjected to aseptic blow molding and charged into a container, the open end of the container is sealed, and the packaged curd product is ultimately heated for coagulation. There has also been shown in the Japanese Patent Kokoku No. 56-39865 a method according to which, in the above described method, the soy bean milk is continuously and homogeneously mixed with the coagulant (GDL).
With these prior-art methods, the coagulant used (GDL) is of the type that needs to be heated to solidify the soy bean milk. As a result thereof, should the coagulant be added to the soy bean milk prior to UHT method (for example VTIS method) sterilization process, it is coagulated by the heat evolved during the sterilization process. Therefore, as a matter of course, the coagulant cannot be added to the soy bean milk prior to the sterilization process. Thus, in the aforementioned Japanese Patent Kokoku No. 56-23574, it is stated that the coagulant is added to the resulting sterilized soy bean juice or to the said sterilized soy bean milk meaning that the coagulant need be added after the sterilization process.
Addition of a large quantity of the coagulant in this manner after the sterilization process tends to pose a problem in the aseptically controlled operation of the production process. Thus a sterilizing filter such as Millipore filter as described in the aforementioned publication is required.
Also, in view of the reduced calcium intake in our present-day diet system, it has become a desideratum that a variety of foodstuffs including soy bean milk and soy bean curd be enriched with calcium. With soy bean milk, there is shown in the Japanese Patent Kokoku No. 56-50549 and the Japanese Patent Kokoku Nos. 52-90622, 53-96356 and 53-133669 the method of producing calcium-enriched soy bean milk by adding calcium gluconate or calcium hydroxide to the soy bean milk during the manufacturing process.
However, no other coagulant than GDL has been specified as coagulant in the aforementioned Japanese Patent Kokoku No. 56-23574, No. 23577 or No. 56-39865, in which no suggestion has been made for fortifying the curd with calcium. Addition of a large quantity of a coagulant such as calcium salts other than GDL after the sterilization process also presents difficulties because calcium sulfate, one of the customary coagulants for the soy bean curd, is low in solubility in water and hence cannot be added in large amounts, while calcium chloride, another customary coagulant for the soy bean curd, is coagulates only inhomogeneously and causes deteriorated flavor of the soy bean curd product. Water-soluble calcium salts, such as calcium lactate, can be added in larger quantities after the sterilization process. However, because of the larger relative weight of the lactic acid portion of the calcium lactate molecule, it has to be used in larger quantities when used for calcium fortification. Such addition of the larger quantities of calcium lactate results in a bitter astringent taste thus greatly detracting from the flavor of the soy bean curd. In addition, the product cost is increased due to the higher production cost of calcium lactate.
In this manner, in the preparation of the aseptic soy bean curd products, considerable difficulties are presented in connected with the addition of larger quantities of calcium not only in the flavor and manufacture costs but in the product quality.